The present invention relates to a method of producing paraaminophenol by the electrolytic reduction of nitrobenzene.
Para-aminophenol is produced commercially by the catalytic hydrogenation of para-nitrophenol or nitrobenzene. Its principal use is for the production of the analgesic, para-acetamidophenol. Precious metal catalysts, such as platinum, are required for the catalytic hydrogenation process. The recovery of these catalysts is a significant economic factor in that process.
The electrolytic conversion of nitrobenzene to para-aminophenol has been known for nearly a century. Aniline is a by-product in any process of preparing para-aminophenol from nitrobenzene. U.S. Pat. No. 3,338,806 describes a process for producing para-aminophenol by the reduction of nitrobenzene in an electrolyte of ethanol and sulfuric acid. Other possible products include azoxybenzene, azobenzene, hydrazobenzene, aniline and para-benzidine. This process also produces para-phenetidine as an undesired alcohol by-product and has the further disadvantage of recycling solvent.
U.S. Pat. No. 4,307,249 describes the catalytic production of para-aminophenol from nitrobenzene in an acidic reaction medium containing dimethylalkylamine-N-oxide as a surfactant using a platinum on carbon catalyst. However, the selectivity for para-aminophenol in that process is low, the para-aminophenol to aniline ratio being about 4 or 5 to 1.